1. Field of the Invention
The present invention relates to the placement of large multi-ton prefabricated deck packages (e.g. oil and gas platforms, oil rigs) in an offshore environment upon a usually partially submerged jacket that extends between the seabed and the water surface. Even more particularly, the present invention relates to the use of a moving lifting assembly which is preferably barge supported that can place a very large deck package upon an offshore marine jacket foundation without the use of enormous lifting booms such as form a part of derrick barges, offshore cranes, and the like, and wherein a "quick connect" connection is formed between the lifting assembly and the deck package.
2. General Background
In the offshore oil and gas industry, the search for oil and gas is often conducted in a marine environment. Sometimes the search takes place many miles offshore. Oil and gas well drilling takes place in many hundreds of feet of water depth.
The problem of drilling oil wells offshore and then producing these wells has been solved in part by the use of enormous fixed platform structures with foundations that are mostly submerged, but usually extending a number of feet above the water surface. Upon this foundation (or "jacket" as it is called in the art) there is usually placed a very large prefabricated rig or deck platform. The term "deck platform" as used herein should be understood to include any of a large variety of prefabricated structures that are placed on an offshore jacket foundation to form a fixed offshore platform. Thus, a "deck-platform" can include, e.g. a drilling rig, a production platform, a crew quarters, living quarters, or the like.
A supporting jacket is usually a very large multi-chord base formed of multiple sections of structural tubing or pipe that are welded together. Such jackets have been used for a number of years for the purpose of supporting large deck platforms in an offshore environment.
The jacket or foundation is usually prefabricated on land in a fabrication yard, preferably adjacent to a navigable waterway. The completed jacket can be placed upon a large transport barge so that it can be moved to the drill site where it will be placed upon the ocean floor. As an example, an offshore jacket can be several hundred feet in length. The size of the jacket is of course a function of the depth of water in which the rig will be placed. A five hundred (500) foot water depth at the drill site (or production site) will require a jacket which is approximately 500-550 feet tall. The jacket is usually partially submerged, with only a small upper portion of the jacket extending slightly above the water surface. An offshore jacket as described and in its position on the seabed can be seen, for example, in the Blight, et al U.S. Pat. No. 4,252,469 entitled "Method and Apparatus for installing integrated Deck Structure and Rapidly Separating Same from Supporting Barge Means." Specifically, FIGS. 1, 2 and 3 of the Blight, et al patent show an offshore jacket on the seabed.
A small upper portion of the jacket extends above the water surface. This exposed portion of the jacket is the portion upon which the "deck platform" is placed and supported by. This upper portion of the jacket is usually equipped with a number of alignment devices which enhance the proper placement of the deck package on the jacket. Such alignment devices are referred to variously as stabbing eyes, sockets, or the like. The use of such alignment devices, sockets, or stabbing eyes can be seen in the Blight, et al Pat. Nos. 4,252,468 and 4,252,469 as well as in the Kansan U.S. Pat. No. 4,242,011. For purposes of background and reference, the Kansan U.S. Pat. No. 4,242,011 is incorporated herein by reference. The Blight, et al U.S. Pat. Nos. 4,252,469 and 4,252,468 are likewise each incorporated herein by reference.
Deck platforms can be extremely large and have correspondingly heavy weights. For example, it is not uncommon for a deck platform such as a drilling rig crew quarters, production platform or the like to be between five hundred and five thousand (500 and 5,000) tons gross weight. Such enormous load values present significant problems in the placement of deck platforms on offshore jacket structures. First, the placement is done entirely in a marine environment. While the jacket can be laid on its side and/or floated into position, the platform is not a submersible structure, and must be generally supported in an upright condition above the water surface to prevent water damage to the many components that form a part of the drilling or production platform (such as electrical systems, wall constructions, and other portions that will be inhabited by individuals and used as oil and gas well drilling or production equipment).
The art has typically used enormous derrick barges for the purpose of setting or placing deck packages on jackets in an offshore environment. These derrick barges are large, rectangular barge structures with a high capacity lifting boom mounted at one end portion of the deck of the barge. The barge, for example might be three hundred to four hundred (300-400) feet in length, fifty to seventy five (50-75) feet in width, and twenty-five to fifty (25-50) feet deep. These figures are exemplary.
A derrick barge might have a lifting capacity of for example, eight hundred (800) tons. For very large structures such as for example, a fifteen hundred (1500) ton deck package, two derrick barges can be used, each supporting one side portion of the deck platform with a multi-line lift system supported by an enormous structural boom extending high into the air above the package during the lift.
The boom simply works in the same way as in onshore lifting boom, namely the loadline raises and/or lowers the package into its proper position upon the jacket. While the use of such derrick barges has been very successful in the placing of offshore deck packages on jackets through the years, such derrick barges are generally limited in their capacity to packages of two thousand (2,000) tons or less. Further, derrick barges of such an enormous capacity are extremely expensive to manufacture and operate. Many thousand of dollars per hour as a cost of using such a device is not uncommon.
However, when very large loads of, for example 3,000-4,000 tons are involved, the limitation of the derrick barge usually prohibits such a placement on an offshore jacket. In U.S. Pat. No. 4,714,38 issued to Jon Khachaturian there is disclosed a method and apparatus for the offshore installation of multi-ton prefabricated deck packages on partially submerged jacket foundations. The Khachaturian patent uses a variable dimensional truss assembly that is supported by the barge and forms a load transfer interface between the barge and the deck package. Upper and lower connections form attachments between the truss members and the deck package at upper and lower elevational positions on the deck package. The variable dimension truss includes at least one member of variable length, in the preferred embodiment being a winch powered cable that can be extended and retracted by winding and unwinding the winch. Alternate embodiments include the use of a hydraulic cylinder as an example.
An earlier patent, U.S. Pat. No. 2,598,088 issued to H. A. Wilson entitled "Offshore Platform Structure and Method of Erecting Same" discusses the placement of drilling structure with a barge wherein the legs of the drilling structure are placed while the drilling structure is supported by two barges. The Wilson device does note use truss-like lifting assemblies having variable length portions which are placed generally on opposite sides of the deck package. Rather, Wilson relates to a platform which is floated in place and the support legs are then placed under the floating platform. Thus, in the Wilson reference, an in-place underlying supporting jacket is not contemplated.
The Natvig, et al U.S. Pat. No. 3,977,346 discusses a method of placing a deck structure upon a building site such as a pier. The method includes the pre-assembly of a deck structure upon a base structure on land so that the deck structure extends outwardly over a body of water. Floating barges are provided for supporting the deck structure outwardly of the building site. The deck structure is then transferred to the supportive base structure by means of barges. The Natvig reference uses two barges which are placed on opposite sides of a platform with pedestal type fixed supports forming a load transfer member between the barges and the platform. However, the fixed pedestal of Natvig are unlike the truss-like lifting arrangement of applicant which include movable portions at least one of which can be of a variable length.